Vehicle seat

ABSTRACT

Vehicle seat including: a seat back pivoted to a side of floor; a seat cushion pivoted to the seat back; and a front leg element having an upper end pivoted to the seat cushion and a lower end pivotally locked to the side of floor in a releasable manner, thus normally providing a four-pivotal-point linkage in the seat. Maintaining the four-pivotal-point linkage adversely restricts design and actions of the seat. Inequality conditions are therefore set in that four-pivotal-point linkage, such that folding down the seat back by an angle exceeding a predetermined angle results in unlocking of the lower end of the front leg element from the side of floor, thereby destroying the four-pivotal-point linkage. Hence, a freedom of design is increased for the seat and floor. Further, leverage mechanism(s) may be provided to facilitate the ease of unlocking the front leg element from the side of floor.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a vehicle seat of the type wherein itsseat cushion and seat back are operatively interconnected via a linkagearranged among pivotal points associated with the seat cushion, the seatback and a floor of vehicle. The seat back can be folded onto the seatcushion, with the rear surface of the seat back being exposed upside,and thereafter, the seat cushion with the seat back folded thereon bedisplaced to a storage position, so that the rear surface of the seatback can be used as a loading area or baggage loading area in thevehicle including an automobile.

2. Description of Prior Art

One example of conventional vehicle seats of this kind is disclosed inJapanese Laid-Open Patent Publication 2005-067325 (JP 2005-067325 A1).As shown therein, four pivotal points are defined in the followingfashion: i) a lower end portion of a seat back frame is pivotallyconnected to a seat slide device's upper rail fixed on a floor, thusproviding a first pivotal point; ii) a rear end portion of a seatcushion frame is pivotally connected to the seat back frame, thusproviding a second pivotal point; iii) a front link is at its upper endpivotally connected to a front end portion of the sea cushion frame,thus providing a third pivotal point; and iv) a lower end of the frontlink is pivotally secured to the floor, thus providing a fourth pivotalpoint.

Due to such four pivotal points, a parallel linkage is established amongthe seat back frame, seat cushion frame, front link, and floor, so that,whenever the seat is folded and moved forwardly and rearwardly, the seatcushion frame and the floor are always maintained in parallel with eachother, while the front link and the seat back frame's lower end portionare also always maintained in parallel with each other.

In this sort of seat, however, it is required for a technical designerto set the front link or the afore-said fourth pivotal point within alimited range of positions in order to insure maintaining the parallellinkage described above. Further, the fact that the lower end of thefront link has a fixed pivotal connection with the floor necessitatesthe designer to consider a degree of load that will be directly appliedto the front link and adjustingly set a position of the front link'supper end to the seat cushion frame, depending on such degree of load,while insuring that the parallel linkage is maintained. As such, settinga position of the front link to the seat cushion frame and floor (i.e.the third and fourth pivotal points) is actually limited, which means aless freedom of setting the front link thereto, thus limiting a freedomof design for the seat. Moreover, the seat of this Japanese prior artrequires forward and rearward sliding of the seat back via upper andlower rails of the seat slide devices to permit forward folding of theseat back onto the seat cushion completely. Consequently, when the upperrail is locked to the lower rail, the seat back is thereby limited as toits forward folding and can be folded at a small angle of inclination,and therefore, under the locked state of seat slide devices, the seatback can not completely be folded down to the seat cushion.

SUMMARY OF THE INVENTION

In view of the afore-stated drawbacks, it is a primary purpose of thepresent invention to provide a vehicle seat of the type having afour-pivotal-point linkage, which makes it possible to increase afreedom of setting a leg element thereof to a seat cushion, therebyincreasing a freedom of design for the seat.

In order to achieve such purpose, in accordance with the presentinvention, there is provided a vehicle seat for use with a vehiclehaving a floor therein, which basically comprises:

a seat back frame provided in a seat back, the seat back frame being ata lower end thereof pivotally connected to the floor, thus defining afirst pivotal point between the seat back frame and the floor;

a seat cushion frame provided in a seat cushion, the seat cushion framebeing at a rearwardly-facing end thereof pivotally connected to the seatback frame, thus defining a second pivotal point between therearwardly-facing end of the seat cushion frame and the seat back frame;

a leg element having an upper end pivotally connected to a forwardportion of the seat cushion frame at a point anteriorly of the secondpivotal point, thus defining a third pivotal point between the upper endof the leg element and the seat cushion frame; and

a lock device fixedly disposed at the floor,

wherein a lower end portion of the leg element is releasably engaged inthe lock device, thereby being normally in a locked relation with thefloor, thus defining a fourth pivotal point between the lower endportion of the leg element and the floor.

In other words, the first, second, third and fourth pivotal pointsestablish a four-pivotal-point linkage among the seat back frame, theseat cushion frame, the front leg element and the floor. Thisfour-pivotal-point linkage is normally maintained, but, when the seatback frame is rotated forwardly and downwardly relative to the firstpivotal point by an angle exceeding a predetermined angle, the lower endof the leg element is disengaged from the lock device, therebydestroying the four-pivotal-point linkage.

Accordingly, the leg element, which restricts the design and actions ofthe seat having this kind of four-pivotal-point linkage, can be releasedfrom the fourth pivotal point, which destroys the four-pivotal-pointlinkage. This allows increasing of a freedom of setting the leg elementto the seat cushion, thereby increasing a freedom of design for theseat, and further allows both seat cushion and seat back to becompletely folded down towards the floor, irrespective of whether a seatslide device or other elements may be provided between the seat andfloor.

Preferably, the lock device may be so formed to include an engagementportion defined inside thereof and a resiliently biasing portion, withsuch an arrangement that the lower end portion of the front leg elementis normally engaged in the engagement portion of the lock device andprevented by the resiliently biasing portion from being removed from theengagement portion and that the lock device permits the lower endportion of the front leg element to be drawn and disengaged from theengagement portion thereof against a biasing force of the resilientlybiasing portion, while permitting the lower end portion to be insertedand engaged in the engagement portion thereof against the biasing forceof the resiliently biasing portion.

As one aspect of the invention, the seat may include an element withwhich a lower part of the front leg element near to the fourth pivotalpoint is to be contacted, thereby limiting movement of the front legelement at the element, wherein the element is defined at or adjacent tothe floor and forms a fulcrum. Further, the third pivotal point may forma point of force application, to which a force is to be applied from theseat back frame, and the lower end portion of the front leg element mayform a point of action against the lock device, whereupon a leverage isprovided to the front leg element. When the seat back frame is rotatedforwardly and downwardly relative to the first pivotal point by an angleexceeding a predetermined angle, the lower part of the front leg elementcomes into contact with the element, whereby the force applied from theseat back frame is amplified under the leverage to facilitatedisengagement of the lower end portion of the front leg element from thelock device.

Essentially, the above-described four-pivotal-point linkage may bearranged such that, letting a first distance to be set between the firstand second pivotal points, letting a second distance to be set betweenthe second and third pivotal points, letting a third distance to be setbetween the third and fourth pivotal points, and letting a fourthdistance to be set between the fourth and first pivotal points, a sum ofthe first and second distances is not equal to or not smaller than a sumof the third and fourth distances.

Preferably, a guide element may be disposed between the lock device andthe floor, the guide element being so configured and sloped as to allowthe end portion of the front leg element to be guided therealong in adirection from the lock device towards the floor. This d guide elementincludes: an upper end portion disposed adjacent to and anteriorly ofthe lock device; and a lower end portion extending downwardly and aslanttowards the floor.

As another aspect of the invention, an under cover may be providedbetween the seat cushion frame and the floor, the under cover includinga guide portion disposed between the lock device and the floor, whereinthe guide portion is so configured and sloped as to allow the endportion of the front leg element to be guided therealong in a directionfrom the lock device towards the floor. Such guide portion includes: anupper end portion disposed adjacent to and anteriorly of the lockdevice; and a lower end portion extending downwardly and aslant towardsthe floor.

In addition, the under cover may be so formed to include a portion withwhich a lower part of the front leg element near to the fourth pivotalpoint is to be contacted, thereby limiting movement of the front legelement at the portion, wherein the portion forms a fulcrum. The thirdpivotal point forms a point of force application, to which a force is tobe applied from the seat back frame. The lower end portion of the frontleg element forms a point of action against the lack device. In thatmanner, a leverage is provided to the front leg element. When the seatback frame is rotated forwardly and downwardly relative to the firstpivotal point by an angle exceeding a predetermined angle, the lowerpart of the front leg element comes into contact with the portion of theunder cover, whereby the force applied from the seat back frame isamplified under the leverage to facilitate disengagement of the lowerend portion of the front leg element from the lock device.

Preferably, an auxiliary leg element may be provided to a bottom side ofa forwardly-facing end portion of the seat cushion frame so as to besuspended therefrom.

As still another aspect of the invention, a seat for use with a vehiclehaving a floor therein may be comprised of:

a seat slide device operable for adjustment in position of the seat inforward and rearward directions of the seat, the seat slide deviceincluding: a lower rail element fixedly mounted on the floor; and anupper rail element slidably engaged with the lower rail element;

a seat back frame provided in a seat back, the seat back frame being ata lower end thereof pivotally connected to the upper rail element of theseat slide device, thus defining a first pivotal point between the seatback frame and the upper rail element;

a seat cushion frame provided in a seat cushion, the seat cushion framebeing at a rearwardly-facing end thereof pivotally connected to the seatback frame, thus defining a second pivotal point between the seatcushion frame and the seat back frame;

a leg element having an upper end pivotally connected to a forwardportion of the seat cushion frame at a point anteriorly of the secondpivotal point, thus defining a third pivotal point between the upper endof the leg element and the seat cushion frame; and

a lock device fixedly disposed at a location substantially correspondingto the upper rail element;

wherein a lower end of the leg element is releasably engaged in the lockdevice, thereby being normally in a locked relation with the upper railelement of the seat slide device, thus defining a fourth pivotal pointbetween the lower end of the leg element and the upper rail element.

This mode of seat incorporating the seat slide device may also bechanged in its parts and elements in substantially the same way asdescribed in the preceding modes.

Other various features and advantages will become apparent from readingof the description, hereinafter, with reference to the accompanieddrawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of a vehicle seat to which a principal partof the present invention is applied, in association with a firstexemplary embodiment of the invention;

FIG. 2 is a perspective view showing a framework of vehicle seat inaccordance with the first embodiment, wherein a seat slide device isprovided;

FIG. 3 is a front view of the first embodiment of vehicle seatframework;

FIG. 4 is a side elevation view of the vehicle seat framework, whichshows a linkage relation among four pivotal points provided therein;

FIG. 5 is a diagram for explanatorily showing a state where a front legelement is released from a fourth pivotal point, thereby destroying thelinkage relation, when a seat back frame is inclined and moveddownwardly by an angle exceeding a predetermined angle;

FIG. 6 is a fragmentary cross-sectional view of a principal part of theinvention in accordance with the first embodiment, which shows a statewhere a male engagement portion of the front leg element is engaged in alock device;

FIG. 7 is a fragmentary cross-sectional view of the principal part ofthe invention in accordance with the first embodiment, whichexplanatorily shows a state where the male engagement portion is aboutto be disengaged from the lock device;

FIG. 8 is a diagram showing a state where both seat cushion frame andseat back frame folded thereon are stored at a second floor area, inaccordance with the first embodiment;

FIG. 9 is a partly broken schematic perspective view showing a secondembodiment of the present invention, wherein an under cover is providedbetween the seat cushion frame and seat slide device;

FIG. 10 is a sectional view taken along the line X-X in the FIG. 9;

FIG. 11 is a fragmentary cross-sectional view of a principal part of theinvention in accordance with the second embodiment, which shows a statewhere the male engagement portion of the front leg element is engaged inthe lock device;

FIG. 12 is a fragmentary cross-sectional view of the principal part ofthe invention in accordance with the second embodiment, whichexplanatorily shows a state where the male engagement portion isdisengaged from the lock device and moved on a guide surface region ofthe under cover;

FIG. 13 is a diagram showing a state where a front end portion of theseat cushion frame comes into contact on the second floor area, whilethe male engagement portion is still moved on the lower end region ofthe under cover, in accordance with the second embodiment;

FIG. 14 is a diagram showing a state where both seat cushion frame andseat back frame folded thereon are stored at the second floor area, inaccordance with the second embodiment;

FIG. 15 is a diagram showing a third embodiment of the invention, whichindicates that a pedestal may be provided between the vehicle seat andthe first floor area, in place of the seat slide device;

FIG. 16 is a diagram showing a fourth embodiment of the invention, whichindicates that an under cover may be provided so as to cover a whole ofthe pedestal shown in the FIG. 15; and

FIG. 17 is a diagram showing a state where an auxiliary support elementof the seat cushion frame is first contacted on a second floor area,while the male engagement portion is still being engaged in the lockdevice.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS OF THE INVENTION

FIG. 1 shows, in perspective, one exemplary mode of vehicle seat inaccordance with the present invention. Throughout all the Figures, thevehicle seat per se is generally designated by 1, which includes a seatcushion SC and a seat back SB foldable forwardly and downwardly onto theseat cushion SC. Designation 3 denotes a reclining device operable toadjustably incline the seat back SB relative to the seat cushion SC.

Hereinafter, it is noted that the wording, “forward”, “forwardly” and“front”, refer to a direction toward a forward side FR of the seat 1,whereas the wording, “rearward”, “rearwardly” and “rear”, refer to adirection toward a rearward side RR of the seat 1.

First of all, in all the embodiments to be hereinafter described, thevehicle seat 1 of the present invention is based on a four-pivotal-pointlinkage mechanism which includes one releasable pivotal point among thefour pivotal points thereof. Namely, referring FIGS. 2 to 4 inconjunction with FIG. 1, it is to be understood generically that:

-   -   a) the seat back SB is at its lower end portion (at 7 b)        pivotally connected to a side of floor (at F1), thus providing a        first pivotal point (at 11);    -   b) the seat cushion SB is at its rear end portion (at 6 b)        pivotally connected to a lower end portion of the seat back SB,        thus providing a second pivotal point (at 12);    -   c) a front leg element 10 is at its upper end portion pivotally        connected to a forward portion of the seat cushion, thus        providing a third pivotal point (at 13); and    -   d) the front leg element 10 is its lower end portion pivotally        connected to a forward end portion of load-receiving support        element 16 fixed on a side of floor (at F1), thus providing a        fourth pivotal point (at 21) which is a releasable pivotal point        to be discussed later.

As will become apparent later, this four-pivotal-point linkage hasunique construction and effects for achieving an increased freedom ofdesign and advantageous aspects in the vehicle seat of this kind.

Now, with reference to FIGS. 1 to 8, a description will be made of afirst embodiment of the vehicle seat 1 in accordance with the presentinvention, wherein the vehicle seat is equipped with a pair of knownseat slide devices 2 and 2 for permitting forward and reward adjustmentin position of the seat.

A seat cushion frame 6 and a seat back frame 7 are provided in the seatcushion SC and the seat back SB, respectively. The seat cushion frame 6includes: a substantially-U-shaped front tubular frame portion 6 a; anda pair of lateral frame portions 6 b and 6 b extending from two ends ofthat front tubular frame portion 6 a, respectively. The seat back frame7 includes: a substantially inverted-U-shaped upper tubular frameportion having a pair of lateral frame members 7 a and 7 a; and a pairof lower frame portions 7 b and 7 b.

As shown, each of the afore-said seat slide devices 2 and 2 comprises: alower rail 2 a which may be fixed on either a planar floor FL (see FIG.4) or a first floor area F1 (see FIGS. 2 and 8): and an upper rail 2 bslidably engaged with the lower rail 2 a. Though not shown, a known lockmechanism is installed in those seat slide devices, so that operation ofthe lock mechanism causes locking and unlocking of the upper rails 2 bwith respect to the lower rails 2 a for the purpose of locking thevehicle seat 1 at a desired position in the forward and rearwarddirections.

The two lower frame portions 7 b and 7 b of the seat back frame 7 arepivotally connected via two first pins 11 to the afore-said two upperrails 2 a and 2 b of the seat slide device 2, respectively. In otherwords, it is defined hereby that a pair of first pivotal points (at 11and 11) are provided between the seat back frame 7 and the seat slidedevice 2 in a symmetrical manner relative to a center of the seat 1.

The two lateral frame portions 6 b and 6 b of the seat cushion frame 6are pivotally connected via two second pins 12 to the two lower frameportions 7 b and 7 b of the seat back frame 7, respectively, at alocation above the foregoing two first pins 11. In other words, it isdefined hereby that a pair of second pivotal points (at 12 and 12) areprovided between the seat cushion frame 6 and the seat back frame 7 in asymmetrical manner relative to a center of the seat 1.

Designation 16 denotes a load-receiving support element formed from arigid tubular material in the illustrated substantially-U-shapedconfiguration. This load-receiving support member 16 is at its twolateral portions firmly welded to and along the respective two upperrails 2 b and 2 b of the seat slide device 2, and adapted to not onlysupport the front leg element 10, but also receive and absorb a downwardweight or load of an occupant on the seat 1 which will be applieddownwards via the front leg element 10 to the load-receiving supportmember 16.

A pair of auxiliary support legs 25 and 25 are fixedly attached to abottom side of the front cross portion 6 a of the seat cushion frame 6so as to be suspended from a forwardly-facing end portion of the seatcushion SC.

In accordance with the present invention, the front leg element 10 isprovided between the seat cushion frame 6 and the load-receiving supportmember 16. The front leg element 10 is formed by bending a rigid tubularmaterial in a substantially “V” shape or a substantiallyinverted-trapezoidal shape, as illustrated, which defines the followingportions:

-   -   a lower horizontal end portion 10 c, which constitutes a male        engagement portion to be releasably engaged in a female        engagement portion 21 of a lock device 20, as will be explained        later (hereinafter, the lower horizontal end portion 10 c shall        be referred to as “male engagement portion 10 c”); and    -   a pair of upper portions 10 a and 10 a, each having, defined        therein, a rectilinear region 10 a-1 terminating in a free end        which forms an upper free end of the front leg member 10, and an        inclined region 10 a-2 which extends aslant downwardly from the        rectilinear portion 10 a-1 in a direction inwardly of the front        leg element 10 and is integral with the lower horizontal end        portion 10 c.

Specifically, first and second connecting brackets 14 a and 14 b arefirmly welded to the two lateral regions of the front tubular frameportion 6 a of the seat cushion frame 6, respectively. As best shown inFIG. 3, one upper free end portion of the front leg element 10 ispivotally connected by a pin 13 to the first connecting bracket 14 a,whereas the other upper free end of the front leg element 10 ispivotally connected by a pin 13 to the second connecting bracket 14 b,so that the front leg element 10 is rotatably journalled between the twoforward lateral regions of the seat cushion frame 6 in a mannersuspended therefrom. Hence, the front leg element 10 is free to rotateswingingly relative to the pins 13 in forward and rearward directionsunder the seat cushion frame 6. In other words, it is defined herebythat a pair of third pivotal points (at 13 and 13) are provided betweenthe front leg element 10 and the seat cushion frame 6 in a symmetricalmanner relative to a center of the seat 1.

A lock device 20 is fixedly attached via a bracket 20 a to mid area of afront cross portion 16 a of the load-receiving support member 16. As canbe seen in FIGS. 2 and 6, the lock device 20 includes a femaleengagement portion 21 into which a male engagement portion 10 c of thefront leg element 10 may be engaged and retained in a releasable manner.With this lock device 20, normally, the male engagement portion 10 c isrotatably retained in the lock device 20, thereby being rotatably lockedto the load-receiving support member 16 when the seat 1 is set in anormal use position shown in FIGS. 1 and 2. Thus, as far as the frontleg element 10 is locked by the lock device 20 to the load-receivingsupport element 16, both two upper portions 10 a and 10 a of that frontleg element 10 are free to rotate forwardly and rearwardly relative to alongitudinal axis of the male engagement portion 10 c thereof rotatablyengaged in the lock device 20. In other words, under such locked state,a fourth pivotal point (at 10 c and 21) is provided between the frontleg element 10 and the load-receiving support element 16.

As best shown in FIG. 6, for instance, the above-described lock device20 may be formed from a leaf spring material in the illustratedclip-like configuration comprising:

-   -   a female engagement portion 21 so configured to embracingly        receive and accommodate the male engagement portion 10 c of the        front leg element 10 so as to permit rotation of the latter 10 c        therein;    -   a pair of spaced-apart first and second guide pieces 24 a and 24        b upturned from the female engagement portion 21 in a direction        away from each other;    -   a first inwardly-curved region 22 a defined between the first        guide piece 24 a and the female engagement portion 21;    -   a second inwardly-curved region 22 b defined between the second        guide piece 24 b and the female engagement portion 21; and    -   an opening 23 defined between the first and second        inwardly-curved regions 22 a and 22 b, wherein such opening 23        is adapted for allowing ingress and egress therethrough of the        afore-said male engagement portion 10 c into and from the female        engagement portion 21.

Here, the first and second inwardly-curved regions 22 a and 22 b projectinwardly toward each other, but are spaced apart from each other,thereby forming a narrow area between the female engagement portion 21and the two guide pieces 24 a, 24 b, as shown. In such narrow area, theopening 23 is defined. With this constricted or narrow configuration,the male engagement portion 10 c of the front leg element 10, receivedin the female engagement portion 21, is normally blocked and preventedby the two inwardly-curved regions 22 a and 22 b from being removed fromthe lock device 20.

The female engagement portion 21 is of a substantially channelcross-section as viewed from FIG. 6 in which the lower horizontalportion or male engagement portion 10 c of the front leg element 10 maybe rotatably accommodated. As will be elaborated later, the front legelement's male engagement portion 10 c can be engaged and disengaged inand from the lock device's female engagement portion 21 at the time whena user executes an operation for folding both seat back SB and seatcushion SC downwardly onto either the planar floor FL (see FIG. 4) orthe lower floor area F2 (see FIG. 8), or executes a seat cushion tip-upoperation for folding the seat cushion SC upwardly towards the seat backSB.

As understandable from FIGS. 6 and 7, the opening 23 is oriented to theforward side FR in an upwardly angular relation with the femaleengagement portion 21 so as to be located at a locus along which themale engagement portion 10 c of the front leg element 10 is to bedisplaced away from the female engagement portion 21, which will bespecifically described later. In this regard, the male engagementportion 10 c, received in the female engagement portion 21, is enclosedby four walls of the latter 21, excepting the opening 23. Thus, evenwhen a normal upward force is applied, attempting to pull the maleengagement portion 10 c in an upward direction substantiallyperpendicular to the lock device 20, the male engagement portion 10 c ispositively blocked by an upper horizontal wall of the female engagementportion 21 against removal from the lock device.

In brief, to disengage the male engagement portion 10 c from the lockdevice 20, as will be specified later, a user should simply fold theseat back SB downwardly to cause the male engagement portion 10 c todisengage from the female engagement portion 21 against the resilientrepulsive forces of the first and second inwardly-curved regions 22 aand 22 b, so that the female engagement portion 10 c may pass throughtherebetween to the outside of the lock device 20, thereby cancellingthe afore-said fourth pivotal point and destroying thefour-pivotal-point linkage. Conversely, to engage the male engagementportion 10 c with the lock device 20, a user should first place thatmale engagement portion 10 c upon the first and second guide pieces 24 aand 24 b of the lock device 20, and forcibly pass the same 10 c throughbetween those two guide pieces 24 a and 24 b into the inside of thefemale engagement portion 21, whereupon the fourth pivotal point isestablished by those male and female engagement portions 10 c and 21.

With the above-described arrangement, insofar as the male engagementportion 10 c of the front leg element 10 is engaged in the lock devicemale engagement portion 21, all the first pivotal point at 11, secondpivotal point at 12, third pivotal point at 13, and fourth pivotal pointat 10 c and 21 are maintained in the vehicle seat 1, which establishes afour-pivotal-point linkage among the seat back SB, seat cushion SC,front leg element 10 and seat slide device 2. Thus, insofar as suchlinkage is maintained, a user can move the seat back SB forwardly andrearwardly within a limited range to cause simultaneous forward andrearward rotation of both front leg element 10 and seat cushion SCrelative to the lock device 20.

In this regard, with reference to FIG. 4, the four-pivotal-point linkagecan be observed imaginarily by the four solid lines which are designatedby D1, D2, D3 and D4, respectively,

wherein

-   -   the designation D1 represents a first distance between the first        pivotal point (at 11) and the second pivotal point (at 12);    -   the designation D2 represents a second distance between the        second pivotal point (at 12) and the third pivotal point (at        13);    -   the designation D3 represents a third distance between the third        pivotal point (at 13) and the fourth pivotal point (at 10 c and        21); and    -   the designation D4 represents a fourth distance between the        fourth pivotal point (at 10 c and 21) and the first pivotal        point (at 11).

In accordance with the present invention, the following conditions areset:

A sum of the first and second distances D1 and D2 is not equal to andnot smaller than a sum of the third and fourth distances D3 and D4, asexpressed by the following inequality: D1+D2>D3+D4

The second distance D2 is not smaller than the fourth distance D4, asexpressed by the following inequality: D2>D4

Because of the inequality D1+D2>D3+D4, a diagonal distance between thesecond pivotal point (at 12) and the fourth pivotal point (at 10 c and21) is greater than a diagonal distance between the first pivotal point(at 11) and the third pivotal point (at 13), as can be seen in FIG. 4.With forward-and-downward folding of the seat back frame 7, the formerdiagonal distance between the second and fourth pivotal points (at 12)and (at 10 c and 21) becomes smaller than the distance D2, while thatdistance D2 remains unchanged, within the four-pivotal-point linkageThis greatly increases an upward displacement of the third pivotal point(at 13) from the fourth pivotal point (at 10 c and 21), so that, uponthe seat back frame 7 being folded by an angle of inclination exceedinga predetermined angle, the male engagement portion 10 c of the front legelement 10 is forcibly pulled upwards and disengaged from the lockdevice's female engagement portion 21.

Only the fourth pivotal point (at 10 c and 21) may be cancelled, sincethe male engagement portion 10 c is releasable from the lock device'sfemale engagement portion 21 as stated above, to thereby permitdestroying the four-pivotal-point linkage in the seat 1.

Accordingly, the four-pivotal-point linkage in the present invention isarranged irregularly in contrast to the parallel linkage relationmaintained in the conventional seats.

First of all, as briefly stated above, a primary aspect of the presentinvention is to provide an increased freedom of design for this sort ofvehicle seat. For that purpose, inventors of the present invention havecome up with the above-described unique linkage in the vehicle seat 1 toincrease freedom of setting the front leg element 10 to the seat cushionframe 6.

Hereinafter, a description in this regard will be given specificallywith reference to FIGS. 4 to 8, by way of one example, based on theabove-defined four conditions.

Suppose now that the seat back frame 7 is folded forwardly anddownwardly under a force F applied from a user and that the inclinationangle of the seat back frame 7 exceeds a predetermined angle θ, as shownin FIG. 5. Then, under the above-described unique linkage, the seatcushion frame 6 is first subjected to extreme forward-and-upwarddisplacement. In other words, the third pivotal point at 13 in the seatcushion frame 6 is moved forwardly beyond the fourth pivotal point (at10 c and 21) due to the inequality D2>D4, with a forward component Cbeing generated from the force F. At the same time, while not clearlyshown, it can be seen from FIG. 5 that, as the diagonal distance betweenthe second and fourth pivotal point (at 12) and (at 10 c and 21) becomessmaller than the distance D2, while that distance D2 remains unchanged,within the four-pivotal-point linkage. This action causes the secondpivotal point at 12 to displace downwardly toward and approach thefourth pivotal point at 10 c and 21, which in turn causes upwarddisplacement of a forward portion of the seat cushion frame 6corresponding to the third pivotal point at 13. In this regard, thediagonal distance between the second and fourth pivotal points (at 12)and (at 10 c and 21) is greater than the diagonal distance between thefirst and third pivotal points (11) and (13), which means that thediagonal distance between the second and fourth pivotal points isparticularly much greater than a corresponding diagonal distance in theconventional four-pivotal-point linkage. Accordingly, in the presentinvention, the upward displacement of the third pivotal point at 13 isgreatly increased as compared with the conventional four-pivotal-pointlinkage, whereby the third pivotal point at 13 is moved far upwardlyaway from the fourth pivotal point at 10 c and 21, with concurrentforward movement of the seat cushion frame 6. Thus, an upward componentB is generated from the force F. With those actions, the male engagementportion 10 c is forcibly pulled forwardly and upwardly from the femaleengagement portion 21, and under the upward and forward components B andC, the male engagement portion 10 c is moved in the direction of arrow Dand pressed against both first and second inwardly-curved regions 24 aand 24 b, which in turn causes those two regions 24 a and 24 b toresiliently warp away from each other, thereby widening the opening 23,as best seen in FIG. 7. As such, the male engagement portion 10 c entersthe widened opening 23 and passes through between the twoinwardly-curved regions 24 a and 24 b to the outside of the lock device20, as understandable in FIG. 5.

In this regard, what is most important aspect is that the front legelement 10 is releasable from the lock device 20 situated at the fourthpivotal points (at 10 c and 21) and displaceable in any of horizontaland vertical directions with respect to either the planar floor FL orthe second floor area F2. In other word, the front leg element 10 is apoint that maintains the four-pivotal-point linkage, which adverselyrestricts the design and actions of the seat 1 as understandable fromthe preceding description of prior art, and if the front leg element 10is releasable from the fourth pivotal point at 10 c and 21, thefour-pivotal-point linkage will be destroyed and nullified, so that anyof the front leg element 10, seat cushion frame 6 and second floor areaF2 can be designed and set in various dimensions and configurations to agreater extent than the conventional fixed-pivotal-point articulationmechanism or parallel linkage mechanism stated in the description ofprior art. Therefore, in the present invention, the male engagementpotion 10 c of the front leg element 10 is releasable from the femaleengagement portion 21 of the lock device, thereby permitting thefour-pivotal-point linkage to be destroyed.

With such arrangement, for example, the following effects areattainable, on the understanding that the front leg element 10, with itsmale engagement portion 10 c engaged in the lock device′ femaleengagement portion 21, has a rigidity for withstanding a maximumtolerable load to be applied thereto.

i) In designing the front leg element 10, the upper end (at 13) thereofcan be set at a desired position in the seat cushion frame 6 in relationto the lock device 20, and also, a length of the front leg element 10 beset in correspondence therewith, as desired, on the condition thatD1+D2>D3+D4.

ii) As indicated by one-dot line in FIG. 4, where one planar floor FL ofvehicle is provided, it is possible to design and form the front legelement 10, seat back frame 7 and seat cushion frame 6, in desired sizeand shape, based on the condition given in the item i) above, so as tonot only permit folding of the seat back SB down onto the seat cushionSC, but also permit displacement of the seat cushion SC with the seatback SB folded thereon in the forward-and-downward direction to apredetermined storage area on the planar floor FL.

iii) As shown in FIGS. 2 and 9, where a first floor area F1 and a secondfloor area F2 are provided, wherein the second floor area F2 is lowrelative to the first floor area F1, it is also possible to design andform the front leg element 10, seat back frame 7 and seat cushion frame,in desired size and shape, based on the condition given in the itemabove, so as to not only permit folding of the seat back SB down ontothe seat cushion SC, but also permit displacement of the seat cushion SCwith the seat back SB folded thereon in the forward-and-downwarddirection to the second floor area F2 (see FIGS. 5, 13 and 14 forexample). Further, the second floor area F2 may be formed deep orshallow (or may be set in height), as desired, with respect to the firstfloor area F1, insofar as the former F2 is not higher than the latterF1, and also, in corresponding therewith, a length of the front legelement 10 be set, as desired, on the condition that D1+D2>D3+D4.

iv) With regard to the item iii) above, both front leg element 10 andsecond floor area F2 may be designed and set in any size and shape,according to size and shape of the seat cushion frame 6 or seat cushionSB.

v) There is no need to move the seat cushion SC via the seat slidedevice 2 to permit folding of the seat back SB onto the seat cushion, asin the conventional seat. This is because, in the present invention, thefourth pivotal point at 10 c and 21 can be cancelled by releasing thefront leg element 10 from the lock device 20, which allows the seat backSB to be completely folded down onto the seat cushion SC, irrespectiveof the upper rail 2 b being lacked to the lower rail 2 a at anyposition. Therefore, in contrast to the conventional vehicle seats, theseat slide device or any other kind of forward-and-rearward adjustmentdevice provided to the vehicle seat 1 do not restrict the movement ofthe seat back SB.

In this context, the pair of the auxiliary support legs 25 and 25 eachcomprises: a downwardly extending portion 25 a which is at its upper endfixed to the seat cushion frame 6; and a contact portion 25 b fixedlyprovided to a lower end of that downwardly extending portion 25 a. Thosetwo auxiliary support legs 25 and 25 are disposed in the seat cushionSC, such that both two contact portions 25 b projects downwardly fromthe underside of the seat cushion SC, as seen in FIG. 1. In the processof folding and displacing both seat cushion frame 6 and seat back frame7 to either a predetermined storage area in the planar floor FL or thesecond floor area F2, the two contact portions 25 b and 25 b respectiveof the two auxiliary support legs 25 and 25 are first brought intocontact with either the planar floor FL or the second floor area F2, asunderstandable from FIG. 17, thereby avoiding any damage and injury tothe outer forward surfaces of the seat cushion SC and also preventingthe seat cushion SC from being stained by dirt and dust on either theplanar floor FL or the second floor area F2.

In addition to the above-described main aspect of the present invention,other remarkable aspects of the invention will be set forth as below.

a) As can be seen from FIG. 5 in conjunction with FIG. 4, as far as thesea back frame 7 is rotated forwardly and downwardly relative to thefirst pivotal point (at 11) by an angle of inclination which is notgreater than the predetermined angle θ, the front leg element 10 as wellas its upper pivotal point (at 13) may be rotatively displaced forwardlyrelative to the longitudinal axis of the male engagement portion 10 crotatably engaged in the female engagement portion 21. Under suchcondition only, a four-pivotal-point linkage (at D1, D2, D3 and D4) ismaintained among the seat back frame 7, seat cushion frame 6, front legelement 10 and seat slide device 2, so that the male engagement portion10 c is maintained in engagement with the lock device 20, thus keepingthe front leg element 10 in a locked relation with the load-receivingsupport element 16. In other words, a certain play is given to theforward and rearward movements of both seat cushion SC and seat back SB,prior to a user completely folding down the seat back SB onto the seatcushion SC for displacement thereof to either a predetermined storagearea in the planar floor FL or the second floor area F2.

b) Now, suppose that the seat back frame 7 is folded forwardly anddownwardly by an angle of inclination exceeding the predetermined angleθ, as shown in FIG. 5. In that case, due to the linkage discussed aboveand also due to a leverage aspect of the seat back frame 7 to beexplained later, forward and upward forces are applied to the seatcushion frame 6 in a greatly amplified manner.

In brief, as indicated in FIG. 5, a forward-and-downward force F appliedby a user from the seat back frame 7 is transmitted through the linkage(at D1, D2, D3 and D4) towards the front leg element 10 and transformedinto a forward-and-upward force having a forward component C and anupward component B, such that the forward component C attempts todisplace the third pivotal point (at 13) far forwardly beyond the fourthpivotal point (at 10 c and 21) where the lock device 20 lies, while atthe same time, the upward component B attempts to displace that thirdpivotal point (at 13) far upwardly from the fourth pivotal point (at 10c and 21).

More specifically, with forward and downward folding of the seat backframe 7 by an angle exceeding the predetermined angle θ under the forceF, the seat cushion frame 6 is subjected to extreme forward-and-upwarddisplacement through the above-described unique linkage, to the extentthat: i) the third pivotal point at 13 in the seat cushion frame 6 isbrought onward past the fourth pivotal point at 10 c and 21 due to theinequality D2>D4, with the forward component C being generated from theforce F, and ii) at the same time, the diagonal distance between thesecond and the fourth pivotal points (at 12) and (at 10 c and 21)becomes smaller than the distance D2, while that distance D2 remainsunchanged, within the four-pivotal-point linkage, with the result thatthe third pivotal point (at 13) is moved in upward direction away fromthe fourth pivotal point (at 10 c and 21), with the upward component Bbeing generated from the force F.

As a consequence thereof, the male engagement portion 10 c is forciblypulled forwardly and upwardly from the female engagement portion 21 by acertain angle relative to a bottom of the latter 21. Here, a locusexists, along which the male engagement portion 10 c is to be displacedaway from the female engagement portion 21 in the forward and upwarddirections. As stated previously, the opening 23 of the lock device 20is situated at such locus, for which any person skilled in the art canunderstand by looking at FIGS. 5, 6 and 7. Therefore, under the upwardand forward components B and C, the male engagement portion 10 e ismoved along the said locus in the direction of arrow D and preciselypressed against both first and second inwardly-curved regions 22 a and22 b, whereupon those two regions 22 a and 22 b are resiliently warpedaway from each other by that male engagement portion 10, against theirbiasing forces, thereby widening the opening 23, as best seen in FIG. 7.Consequently, the male engagement portion 10 c smoothly enters thewidened opening 23 and passes through between the two inwardly-curvedregions 22 a and 22 b to the outside of the lock device 20, as seen inFIG. 5.

c) In connection with the item b) above, it is importantly added thatthe force F applied to the seat back frame 7 is amplified by a leverageprovided among the seat back frame 7, seat cushion frame 6 and seatslide device 2, and the amplified force will be transmitted through thefour-pivotal-point linkage towards the male engagement portion 10 c.Referring to FIG. 5, such leverage will be described. When a user pushesand moves a top portion of the seat back SB or a top portion of the seatback frame 7 forwardly and downwardly, a particular point in that seatcushion frame's top portion, pushed by the user, forms a point of forceapplication FP. A distance between the top portion of the seat cushionframe 7 and the second pivotal point 12 is over twice or three time asgreat as a distance between the second pivotal point 12 and the firstpivotal point 11. Therefore, as the user folds the seat back frame 7from the point at FP forwardly and downwardly relative to the firstpivot point 11 forming a fulcrum SP, a degree of the force F isamplified in relation to that fulcrum SP and exerted upon the secondpivotal point 12 under the effect of leverage, whereupon that secondpivotal point 12 forms a point of action AP against the third pivotalpoint 13. Namely, the amplified force is transmitted from the secondpivotal point 12 (i.e. the point of action AP) directly to the thirdpivotal point 13 to which the upper end of the front leg element 10 ispivotally connected, thereby attempting to cause that upper end of thefront leg element 10 as well as the front leg element 10 proper to moveforwardly and upwardly in the direction of arrow D. At this point, dueto the above-discussed linkage, the thus-amplified forward-and-upwardforce therefore has the upward and forward components B and C sufficientto overcome the biasing force of the two inwardly-curved regions 22 aand 22 b of the lock device 20. Accordingly, by applying a relativelysmall force to the seat back SB, a user can smoothly cause the maleengagement portion 10 c to pass through between the two inwardly-curvedregions 22 a and 22 b and disengage from the male engagement portion 21of the lock device 20.

By the virtue of the above-described arrangements in the seat 1, when itis desired to fold and move both seat cushion SC and seat back SB toeither a predetermined area in the planar floor FL or the lower floorarea F2, a user may simply fold the seat back SB or the seat back frame7 forwardly and downwardly relative to the first pivotal point 11,whereby the seat cushion SC or the seat cushion frame 6 is displacedforwardly and downwardly, with the front leg element 10 being rotatedforwardly relative to the fourth pivotal point at 10 c and 21.

At this point of time, in the case of the planar floor FL, with furtherforward-and-forward folding of the seat back frame 7, it is to beunderstood, thought not shown, that the front end portion of the seatcushion frame 6 or the two auxiliary support legs 25 and 25 are firstbrought into contact on the planar floor FL before the forwardinclination angle of the seat back frame 7 reaches the predeterminedangle θ, while the male engagement portion 10 c of the front leg element10 is being rotated within the female engagement portion 21 of the lockdevice 20. Thus, during this stage, the front leg element is maintainedin engagement with the lock device 20. Subsequent to the auxiliarysupport legs 25 having contacted the floor FL, when the seat back frame7 is further rotated by an angle exceeding the predetermined angle θ,the male engagement portion 10 c of the front leg element 10 passesthrough between the first and second inwardly-curved regions 22 a and 22b against the biasing forces of the latter and is automaticallydisengaged from the female engagement portion 21. This can be understoodfrom FIGS. 5 and 7. With the forward-and-downward movement of the seatback frame 7, the male engagement portion 10 c rides on and past bothsecond guide pieces 24 b and front cross portion 16 a of theload-receiving support element 16, though not shown. After then, bothauxiliary support legs 25 and male engagement portion 10 c are slidinglymoved on the planar floor FL in the forward direction and stopped at thetime when the seat back frame 7 has been completely folded to afold-down position where it extends adjacent to the seat cushion frame 6in a substantially parallel relation therewith. Thus, it is to beunderstood that both seat cushion SC and seat back SB folded thereon areplaced at a predetermined storage area in the planar floor FL, whereby aspace behind the vehicle seat 1 is widened and the rear surface of theseat back SB may be used as a loading or baggage-loading area in avehicle or automobile.

On the other hand, in the case of the first and second floor areas F1and F2, referring to FIGS. 17 and 8 in sequence, the front end portionof the seat cushion frame 6 or the two auxiliary support legs 25 and 25are first brought into contact on the second floor area F2 before theforward inclination angle of the seat back frame 7 reaches thepredetermined angle θ, while the male engagement portion 100 is beingrotated within the female engagement portion 21. Thus, during thisstage, the front leg element is maintained in engagement with the lockdevice 20. Subsequent to the auxiliary support legs 25 having contactedthe second floor area F2, when the seat back frame 7 is further rotatedby an angle exceeding the predetermined angle θ, the male engagementportion 10 c passes through between the first and second inwardly-curvedregions 22 a and 22 b against the biasing forces of the latter and isautomatically disengaged from the female engagement portion 21. This canbe understood from FIGS. 5 and 7. With further forward-and-downwardmovement of the seat back frame 7, the male engagement portion 10 c isfallen from the first floor area F1 to the second floor area F2 andcontacted on that particular second floor area F2. Then, both auxiliarysupport legs 25 and male engagement portion 10 c are slidingly moved onthe second floor area F2 in the forward direction and stopped at thetime when the seat back frame 7 has been completely folded to afold-down position where it extends adjacent to the seat cushion frame 6in a substantially parallel relation therewith, as seen in FIG. 8.Accordingly, both seat cushion SC and seat back SB folded thereon arestored at the second floor area F2, thereby permitting the rear surfaceof the seat back SB to be used as a loading or baggage-loading area in avehicle or automobile.

Also, when effecting a seat cushion tip-up operation for folding theseat cushion SC or seat cushion frame 6 upwardly to a front side of theseat back SB or seat back frame 7, a user may simply fold the seat backSB or seat back frame 7 downwardly until the male engagement portion 10c of the front leg element 10 is disengaged from the female engagementportion 21 of the lock device 20, which is of course based on theabove-described linkage and leverage. Thereby, the seat cushion SC orseat cushion frame 7 can be unlocked from the lock device 20 and be freeto rotate vertically relative to the second pivotal point at 12. Whenthe user ascertains that the male engagement portion 10 c has beendisengaged from the lock device 20, he or she should stop folding downthe seat back frame 7 and reversely rotate the same 7 back to theupright home position thereof. After then, the user should raise thethus-unlocked seat cushion frame 6 towards the seat back frame 7relative to the second pivotal point at 12, so that the seat cushionframe 6 is positioned on the front side of the seat back frame 7, asindicated by the one-dot chain lines in FIG. 4. Here, the front legelement 10 is in the state of being suspended from the third pivotalpoint at 13 and rested on a bottom side of such upwardly-folded seatcushion frame 6 or seat cushion SB. Accordingly, the front leg element10 does not protrude from the seat cushion SB, whereby a space is fullygiven in front of the thus-folded seat cushion SB and can be used forversatile purposes. In this regard, a suitable lock device may beprovided to the seat back SB for the purpose of locking the front legelement 10 to the side of the seat back SB. It is therefore appreciatedthat the seat cushion tip-up operation can also be easily effected underthe actions of the unique linkage of the present invention.

In this context, as stated previously, the leverage is worked by: theseat back's top portion (at F) forming a point of force application FP;the first pivot point (at 11) forming a fulcrum SP; and the secondpivotal point (at 12) forming a point of action AP. But, in addition tosuch leverage, another second leverage may be provided to the front legelement 10 by simply defining a fulcrum on the side of first floor areaF1, the fulcrum being a point with which the two inclined regions 10 a-2and 10 a-2 of the front leg element 10 are to be contacted when foldingdown the seat back SB towards the seat cushion SC. For example, althoughnot shown, a pair of upwardly-protruding or raised portions may beformed in the front cross portion 16 a of the load-receiving supportelement 16 at points corresponding to the two inclined regions 10 a-2and 10 a-2.

In this connection, reference is made to a second embodiment of FIGS. 9and 12 which shows one example of the afore-stated second leverage thatcan be realized at the front leg element 10. This will be describedspecifically later. In brief, according to this second embodiment, thefulcrum SP is defined at a cumbered top portion 32 of an under cover 30provided to the vehicle seat 1. But, it is to be noted that the secondleverage using the unshown raised portions stated above is identical instructure and actions to the second leverage shown in FIG. 12, onlyexcepting a position of the fulcrum SP. Therefore, while not clearlyshown, but with reference to FIG. 12, the mode of second leverage usingthe unshown raised portions will be described as follows. Namely,looking at the FIG. 12, let us define that each of the unshown tworaised portions defined in the front cross portion 16 a of theload-receiving support element 16 forms a fulcrum SP with respect to thecorresponding one of the two inclined regions 10 a-2 and 10 a-2 of thefront leg element 10, that the third pivotal point 13 at each of the twoupper ends of the front leg element 10 forms a point of forceapplication FP, and that the male engagement portion 10 c of the frontleg element 10 forms a point of action AP against the lock device 20. Inthat way, a second leverage is established to the front leg element 10.Therefore, under such second leverage, in the force F being impartedfrom the point of force FP to each of the two upper ends of the frontleg element 10 under the preceding first leverage, the upward componentB caused to the male engagement portion 10 c (at AP) is particularlyamplified relative to each fulcrum SP between the raised portion and thecorresponding inclined region 10 a-2, for which a person skilled in theart can understand by looking at FIG. 12. Consequently, both first andsecond leverages act on the front leg element 10 at the same time,whereby a far increased upward component B′ is exerted on the maleengagement portion 10 c of the front leg element 10, as compared withthe upward component B caused under the first leverage only. This meansthat the male engagement portion 10 c is provided with a doublyamplified force that exceedingly overcomes the biasing force of thefirst and second inwardly-curved regions 22 a and 22 b of the lockdevice 20. Therefore, with this double leverage effect, a user can applya very small force to the seat back SB to cause the male engagementportion 10 c to pass through between the two inwardly-curved regions 22a and 22 b to the outside of the lock device 20.

FIG. 9 shows a second embodiment of the vehicle seat 1, which suggestsproviding an under cover 30 to the underside of the seat 1, or betweenthe seat cushion frame 6 and the seat slide device 2. In thisembodiment, it should be noted that all the constituent elements andparts described in the foregoing first embodiment are used, exceptingthe under cover 30 only. Therefore, all like designations to be givenhereinafter correspond to all like designations used in the foregoingfirst embodiment, and any further description is omitted as to thecommon elements and parts between the first and second embodiments.

As with the conventional art, the under cover 30 itself indeed concealsa corresponding area of the first floor area F1 under the seat 1,including the load-receiving support element 16, the lock device 20 andmost of the seat slide rail 2, with a view to improving an aestheticappearance of the underside of the seat 1. But, in addition thereto, theunder cover 30 of the present invention functions to guide the front legelement 10 towards the lock device 20 and also guide the same 10 awayfrom lock device 20 in a direction to the second floor area F2. Further,the under cover 30 functions to retain the front leg element 10 againstmovement and wobbling, when the male engagement portion 10 c is engagedwith the lock device 20. For that purpose, the under cover 30 is formedwith the following regions:

-   -   an opening region 33 defined in the front side of the under        cover 30 at a location where the lock device 20 exists;    -   an inner wall region 33 d defined within the under cover 20        posteriorly of the opening region 33, the inner wall region        being adapted to receive and support the first and second        inclined regions 10 a-2 and 10 a-2 of the front leg element 10;    -   a pair of spaced-apart notch regions 33 a and 33 a defined in        the outer surface 33 c of the under cover 30 at a location above        the opening region 33;    -   a sloped surface region 31 extending forwardly from the opening        region 33 in a downward direction to the second floor area F2,        wherein the sloped region 31 assumes a cambered contour as        shown;    -   a pair of guide surface regions 33 b and 33 b adjoining with and        along the two lateral sides of the sloped surface region 31,        respectively; and    -   a lower end region 31 a of substantially tongue or “U” shape        which extends continuously from the sloped surface region 31 in        a downward direction to either the second floor area F2 or the        planar floor FL.

Specifically, the opening region 33 is so configured to allow ingressand egress therethrough of both male engagement portion 10 c and lowerinclined portions 10 a-2 of the front leg element 10 into and from theinside of the under cover 30. As best shown in FIG. 11, inside of suchopening region 33, the under cover 30 is provided with an inner recessedarea that surrounds or houses substantially a whole of the lock device20. Designation 33 h denotes a hole formed in such inner recessed areaof the under cover 30. This hole 33 h allows both two guide pieces 24 aand 24 b of the lock device 20 to move and pass therethrough freely inoutward and inward directions.

The sloped region 31 is shown to be recessed downwards from the outersurface 33 c of the under cover 30. This particular sloped region 31includes a cambered top portion 32 situated in the proximity of theopening region 33, wherein such cambered top portion 32 has an upwardlycurved cross-section as viewed from FIG. 11. Note that the sloped region31 has a width slightly larger than an entire length of the maleengagement portion 10 c of the front leg element 10.

Defined between the recessed sloped region 31 and the outer surface 33 care the two guide surface regions 33 b and 33 b, each being slopeddownwardly in a direction from the outer surface 33 c to the slopedregion 31. Note that an angle of inclination of each of suchdownwardly-sloped guide surface regions 33 b is substantially equal toan angle of inclination of each of the inclined regions 10 a-2 of thefront leg element 10. As observed in FIG. 9, the pair of guide surfaceregions 33 b and 33 b extend upwardly, while increasing their respectiveareas progressively, and terminate in the pair of notch regions 33 a and33 a, respectively.

Each of the two notch regions 33 a and 33 a is so configured anddisposed as to receive and retain a local part of each of the twoinclined regions 10 a-2 and 10 a-2 therein, as best seen in FIG. 9.

When the front leg element 10 is locked by the lock device 20 to theload-receiving support element 16, the male engagement portion 10 c is,of course, embracingly retained in the female engagement portion 21 ofthe lock device 20. Under this locked state, as shown in FIGS. 9, 10 and11, the two inclined regions 10 a-2 and 10 a-2 of the front leg element10 are partly engaged in the two notch regions 33 a and 33 a,respectively, whereby both front leg element 10 and seat cushion frame 6are positively prevented from being moved and wobbled in the lateraldirection (or left and right directions) thereof.

When a user folds the seat back SB or the seat back frame 7 forwardlyand downwardly as indicated by the arrow in FIG. 5, the seat cushionframe 6 is automatically displaced in the arrow direction A under thepreviously described linkage, which in turns causes forward rotation ofthe front leg element 10 relative to the fourth pivotal point at 10 cand 21. At this stage, the same first leverage as explained earlier isnaturally established by the following three points: the top portion ofthe seat back frame 7 as a point of force application FP; the firstpivot point at 11 as a fulcrum SP; and the second pivot point at 12 as apoint of action AP. Hence, under such first leverage, an amplified forceis applied to the third pivotal point at 13, attempting to draw thefront leg element 10 upwardly away from the lock device 20 fordisengagement of the male engagement portion 10 c from the maleengagement portion 21. In the present embodiment, referring to FIG. 12,it is to be understood that both two inclined regions 10 a-2 and 10 a-2of the front leg element 10 are disengaged from the two notch regions 33a and 33 a of the under cover 30, respectively, while being moved awayfrom the inner wall region 33 d on which the two regions 10 a-2 and 10a-2 have been rested, and are brought into contact with the cambered topportion 32 of the under cover 30, prior to disengagement of the maleengagement portion 10 c from the female engagement portion 21. At thismoment, in addition to the first leverage stated above, a secondleverage is caused to the front leg element 10. In other words, aparticular point in the cambered top portion 32, on which the twoinclined regions 10 a-2 of the front leg element 10 are contacted, formsa fulcrum SP. The third pivotal point 13 at the upper end of the frontleg element 10 forms a point of force application FP. The maleengagement portion 10 c of the front leg element 10 forms a point ofaction AP. In that way, the second leverage is established to the frontleg element 10. Therefore, in the force F being imparted from the pointFP to the upper end of the front leg element 10 under the firstleverage, the upward component B caused to the male engagement portion10 c (at AP) is particularly amplified relative to the fulcrum SPbetween the cambered top portion 32 and two inclined regions 10 a-2 and10 a-2, as understandable from FIG. 12. Consequently, both first andsecond leverages act on the front leg element 10 at the same time,whereby a far increased upward component B′ (see FIG. 12) is exerted onthe male engagement portion 100 of the front leg element 10, as comparedwith the upward component B caused under the first leverage only. Thismeans that the male engagement portion 10 c is provided with a doublyamplified force that exceedingly overcomes the biasing force of thefirst and second inwardly-curved regions 22 a and 22 b of the lockdevice 20. Therefore, with this double leverage effect, a user can applya very small force to the seat back SB to cause the male engagementportion 10 c to pass through between the two inwardly-curved regions 22a and 22 b.

Then, the user can continue the downward folding of the seat back SB orseat back frame 7, using his or her small force, with the result thatthe front leg element 10 is moved upwardly and forwardly as indicated bythe arrow D, while the male engagement portion 10 c passes throughbetween the two inwardly-curved regions 22 a and 22 b, as shown in FIG.12. With further downward folding the seat back frame 7, the seatcushion frame 6 advances in the arrow direction A, so that the maleengagement portion 10 c is moved away from the lock device 20 and rideson the cumbered top portion of the sloped region 31 of the under cover30. Thereafter, as indicated by the one-dot chain line in FIG. 12, themale engagement portion 10 c is slidingly moved on the sloped region 31of the under cover 30 in the forward and downward directions, while thetwo inclined regions 10 a-2 and 10 a-2 are being slidingly moved on andalong the two guide surface regions 33 b and 33 b, respectively.

It is to be noted that, instead of the under cover 30, one guide elementmay be provided adjacent to and anteriorly of the lock device 20, theguide element having suitable regions corresponding in shape and size tothe afore-said sloped surface region 31, guide surface regions 33 b, andlower end region 31 a, respectively.

As shown in FIG. 13, the seat cushion frame 6 enters the second floorarea F2 and is automatically rotated downwards thereto, under gravity,relative to the second pivotal point 12, so that both two contactportions 25 b and 25 b of the auxiliary support legs 25 and 25 are firstbrought into contact upon the second floor area F2. At this point oftime, the front leg element 10 is, at its male engagement portion 10 c,still being slidingly moved on the sloped region 31 of the under cover30. Referring to FIG. 14, it can be observed that the seat back frame 7has been folded close to the seat cushion frame 6, while the twoauxiliary support legs 25 and 25 has been slidignly moved forwards onthe surface of the second floor area F2. During those actions, asunderstandable in FIGS. 13 and 14, the male engagement portion 10 c ofthe front leg element 10 further slides on the lower end region 31 a ofthe under cover 30 and is subsequently fallen therefrom toward thesecond floor area F2. Here, it is to be appreciated that a distancebetween the lower end region 31 a and the second floor area F2 is sosmall that an impact given to the male engagement portion 10 c from thesecond floor area F2 is extremely reduced, as opposed to the firstembodiment wherein the male engagement portion 10 c is directly fallenfrom the first floor area F1 to the second floor area F2. Therefore, inthis second embodiment, the male engagement portion 10 c gently contactsthe second floor area F2, so that an objectionable noise generatedtherefrom is nearly eliminated or reduced to a much lower degree than inthe first embodiment.

Subsequently, the seat back frame 7 or the seat back SB is folded ontothe seat cushion frame 6 or the seat cushion SC, while both seat cushionSC and front leg element 10 slidingly advances on the second floor areaF2, with the result that a whole of the seat cushion SC and seat back SBis set and stored at the second floor area F2, as indicated in FIG. 14.

In this connection, instead of the above-described seat foldingoperation, a seat cushion tip-up operation may be done for folding theseat cushion SC upwardly to the seat back SB as indicated by the one-dotchain lines in FIG. 4. In that case, the under cover 30 effectivelyconceals most of the seat slide device 2 as well as a whole portion ofthe first floor area F1 corresponding to the underside of the seatcushion SC that is normally set in the horizontal use position asindicated by the solid lines in FIG. 4, but now folded to a verticalstorage position at the seat back SB as indicated by the one-dot chainlines in FIG. 4. Thus, especially after such seat cushion tip-upoperation, the under cover 30 serves to aesthetically improve an outerappearance of the floor area F1 at the seat 1.

All the foregoing embodiments have been described for the instance wherea forward-and-rearward seat adjustment device, such as the seat slidedevice 2, is applied to the vehicle seat 1. But, in the presentinvention, the seat 1 may be directly, fixedly mounted on either theplanar floor FL or the first floor area F1, without using suchforward-and-rearward seat adjustment device, because the actions of theabove-described unique linkage are in no way dependent on theforward-and-rearward seat adjustment device or the seat slide device 2,but are done solely by folding and unfolding the seat back SB, incontrast to the conventional seat stated in the description of priorart.

As suggested in a third embodiment of FIG. 15, by way of one example,the vehicle seat 1 may be fixedly mounted, via a pedestal 2A, on thefirst floor area F1. In this embodiment, all the constituent elementsand parts described in the first embodiment are used, excepting thepedestal 2A only. Therefore, all like designations to be givenhereinafter correspond to all like designations in the foregoing firstembodiment, and any further description is omitted as to the commonelements and parts between the first and third embodiments. According tothe present third embodiment, the lower end of the seat back frame 7 ispivotally connected to the pedestal 2A. Note that the pedestal 2 a maybe fixed on either the planar floor FL or the shown first floor area F1.The lock device 20 is fixedly attached to the front cross portion 16 aof the load-receiving support element 16 firmly attached as by weldingto the pedestal 2A. All the same actions and effects as described in thefirst embodiment are achievable in this particular third embodiment, forwhich any further description is omitted for the sake of simplicity.

Also, as suggested in a fourth embodiment of FIG. 16, an under cover 30′may be used in the foregoing third embodiment. This under cover 30′ isidentical in structure to the first under cover 30 shown in FIGS. 9 and10, only except that the shape and size of such under cover 30′ is setso as to cover the pedestal 2A. In this fourth embodiment, as can beseen in FIG. 16, a whole of the pedestal 2A is concealed by the undercover 30′, thus improving an outer aesthetic appearance under thevehicle seat 1. Of course, all the same actions and effects as describedin the second and third embodiments are achievable in this fourthembodiment, for which any further description is omitted for the sake ofsimplicity.

While having described the present invention thus far, it should beunderstood that the invention is not limited to the illustratedembodiment, but any modification, replacement and addition may beapplied thereto, without departing from the scope of the appendedclaims.

What is claimed is:
 1. A seat for use with a vehicle having a floortherein, wherein said seat comprises: a seat cushion; and a seat backfoldable forwardly and downwardly onto said seat cushion, comprising: aseat slide device operable for adjustment in position of said seat inforward and rearward directions of the seat, said seat slide deviceincluding: a lower rail element fixedly mounted on said floor; and anupper rail element slidably engaged with said lower rail element; a seatback frame provided in said seat back, said seat back frame being at alower end thereof pivotally connected to said upper rail element of saidseat slide device, thus defining a first pivotal point between said seatback frame and said upper rail element; a seat cushion frame provided insaid seat cushion, said seat cushion frame being at a rearwardly-facingend thereof pivotally connected to said seat back frame, thus defining asecond pivotal point between said seat cushion frame and said seat backframe; a leg element having an upper end pivotally connected to saidseat cushion frame, thus defining a third pivotal point between saidupper end of said leg element and said seat cushion frame; and a lockdevice fixedly disposed at a location substantially corresponding tosaid upper rail element; wherein a lower end of said leg element isreleasably engaged in said lock device, thereby being normally in alocked relation with said upper rail element of said seat slide device,thus defining a fourth pivotal point between said lower end of said legelement and said upper rail element; and wherein said first, second,third and fourth pivotal points establish a four-pivotal-point linkageamong said seat back frame, said seat cushion frame, said front legelement and said floor, wherein said four-pivotal-point linkage isnormally maintained, and wherein, when said seat back frame is rotatedforwardly and downwardly by a first angle relative to said first pivotalpoint, a forwardly-facing end portion of said seat cushion frame isbrought into contact with said floor, with said lower end portion ofsaid leg element being engaged in said lock device, after which, whensaid seat back frame is further rotated forwardly and downwardlyrelative to said first pivotal point by a second angle exceeding apredetermined angle with reference to said first angle, said lower endof said leg element is disengaged from said lock device, therebydestroying said four-pivotal-point linkage.
 2. The seat as claimed inclaim 1, wherein said lock device includes an engagement portion definedinside thereof and a resiliently biasing portion, wherein said lower endportion of said front leg element is normally engaged in said engagementportion of said lock device and prevented by said resiliently biasingportion from being removed from said engagement portion, and whereinsaid lock device is configured such that, when said seat back frame isfurther rotated forwardly and downwardly relative to said first pivotalpoint by said second angle exceeding said predetermined angle, the lockdevice permits said lower end portion of said front leg element to bedrawn and disengaged from said engagement portion thereof against abiasing force of said resiliently biasing portion, while permitting saidlower end portion to be inserted and engaged in said engagement portionthereof against the biasing force of said resiliently biasing portion.3. The seat as claimed in claim 1, which further includes an elementwith which a lower part of said front leg element near to said fourthpivotal point is to be contacted, thereby limiting movement of saidfront leg element at said element, wherein said element is provided ator adjacent to said upper rail element of said seat slide device, saidelement forming a fulcrum, wherein said third pivotal point forms apoint of force application, to which a force is to be applied from saidseat back frame, wherein said lower end portion of said front legelement forms a point of action against said lock device, whereupon aleverage is provided to said front leg element, and wherein, when saidseat back frame is rotated forwardly and downwardly relative to saidfirst pivotal point by said second angle exceeding said predeterminedangle, said lower part of said front leg element comes into contact withsaid element, whereby said force applied from said seat back frame isamplified under said leverage to facilitate disengagement of said lowerend portion of said front leg element from said lock device.
 4. The seatas claimed in claim 1, wherein a first distance is set between saidfirst and second pivotal points, wherein a second distance is setbetween said second and third pivotal points, wherein a third distanceis set between said third and fourth pivotal points, wherein a fourthdistance is set between said fourth and first pivotal points, andwherein a sum of said first and second distances is not equal to a sumof said third and fourth distances.
 5. A seat for use with a vehiclehaving a floor therein, wherein said seat comprises: a seat cushion; anda seat back foldable forwardly and downwardly onto said seat cushion,comprising: a seat back frame provided in said seat back, said seat backframe being at a lower end thereof pivotally connected to said floor,thus defining a first pivotal point between said seat back frame andsaid floor; a seat cushion frame provided in said seat cushion, saidseat cushion frame being at a rearwardly-facing end thereof pivotallyconnected to said seat back frame, thus defining a second pivotal pointbetween said seat cushion frame and said seat back frame; a leg elementhaving an upper end pivotally connected to said seat cushion frame, thusdefining a third pivotal point between said upper end of said legelement and said seat cushion frame; and a lock device fixedly disposedat said floor, wherein a lower end portion of said leg element isreleasably engaged in said lock device, thereby being normally in alocked relation with said floor, thus defining a fourth pivotal pointbetween said lower end portion of said leg element and said side of thefloor, wherein said first, second, third and fourth pivotal pointsestablish a four-pivotal-point linkage among said seat back frame, saidseat cushion frame, said front leg element and said floor, wherein saidfour-pivotal-point linkage is normally maintained, and wherein, whensaid seat back frame is rotated forwardly and downwardly by a firstangle relative to said first pivotal point, a forwardly-facing endportion of said seat cushion frame is brought into contact with saidfloor, with said lower end portion of said leg element being engaged insaid lock device, after which, when said seat back frame is furtherrotated forwardly and downwardly relative to said first pivotal point bya second angle exceeding a predetermined angle with reference to saidfirst angle, said lower end of said leg element is disengaged from saidlock device, thereby destroying said four-pivotal-point linkage.
 6. Theseat as claimed in claim 5, which includes an adjustment device foradjustably positioning said seat in forward and rearward directions ofthe seat, wherein said adjustment device comprises: a lower rail elementfixedly mounted on said floor; and an upper rail element slidablyengaged with said lower rail element, wherein said lower end of saidseat back frame is pivotally connected to said upper rail element, sothat said first pivotal point is defined between said lower end of saidseat back frame and said upper rail element.
 7. The seat as claimed inclaim 5, wherein said lock device includes an engagement portion definedinside thereof and a resiliently biasing portion, wherein said lower endportion of said front leg element is normally engaged in said engagementportion of said lock device and prevented by said resiliently biasingportion from being removed from said engagement portion, and whereinsaid lock device is configured such that, when said seat back frame isfurther rotated forwardly and downwardly relative to said first pivotalpoint by said second angle exceeding said predetermined angle, the lockdevice permits said lower end portion of said front leg element to bedrawn and disengaged from said engagement portion thereof against abiasing force of said resiliently biasing portion, while permitting saidlower end portion to be inserted and engaged in said engagement portionthereof against the biasing force of said resiliently biasing portion.8. The seat as claimed in claim 5, which further includes an elementwith which a lower part of said front leg element near to said fourthpivotal point is to be contacted, thereby limiting movement of saidfront leg element at said element, wherein said element is defined at oradjacent to said floor and forms a fulcrum, wherein said third pivotalpoint forms a point of force application, to which a force is to beapplied from said seat back frame, wherein said lower end portion ofsaid front leg element forms a point of action against said lock device,whereupon a leverage is provided to said front leg element, and wherein,when said seat back frame is rotated forwardly and downwardly relativeto said first pivotal point by said second angle exceeding saidpredetermined angle, said lower part of said front leg element comesinto contact with said element, whereby said force applied from saidseat back frame is amplified under said leverage to facilitatedisengagement of said lower end portion of said front leg element fromsaid lock device.
 9. The seat as claimed in claim 5, wherein a firstdistance is set between said first and second pivotal points, wherein asecond distance is set between said second and third pivotal points,wherein a third distance is set between said third and fourth pivotalpoints, wherein a fourth distance is set between said fourth and firstpivotal points, and wherein a sum of said first and second distances isnot equal to a sum of said third and fourth distances.
 10. A seat foruse with a vehicle having a floor therein, wherein said seat comprises:a seat cushion; and a seat back foldable forwardly and downwardly ontosaid seat cushion, comprising: a seat back frame provided in said seatback, said seat back frame being at a lower end thereof pivotallyconnected to said floor, thus defining a first pivotal point betweensaid seat back frame and said floor; a seat cushion frame provided insaid seat cushion, said seat cushion frame being at a rearwardly-facingend thereof pivotally connected to said seat back frame, thus defining asecond pivotal point between said seat cushion frame and said seat backframe; a leg element having an upper end pivotally connected to saidseat cushion frame, thus defining a third pivotal point between saidupper end of said leg element and said seat cushion frame; and a lockdevice fixedly disposed at said floor, and an auxiliary leg elementprovided to a bottom side of a forwardly-facing end portion of said seatcushion frame so as to be suspended from a bottom side of said seatcushion; wherein a lower end portion of said leg element is releasablyengaged in said lock device, thereby being normally in a locked relationwith said floor, thus defining a fourth pivotal point between said lowerend portion of said leg element and said side of the floor, wherein saidfirst, second, third and fourth pivotal points establish afour-pivotal-point linkage among said seat back frame, said seat cushionframe, said front leg element and said floor, wherein saidfour-pivotal-point linkage is normally maintained, and wherein, whensaid seat back frame is rotated forwardly and downwardly by a firstangle relative to said first pivotal point, said auxiliary leg elementis brought into contact with said floor, with said lower end portion ofsaid leg element being engaged in said lock device, after which, whensaid seat back frame is further rotated forwardly and downwardlyrelative to said first pivotal point by a second angle exceeding apredetermined angle with reference to said first angle, said lower endof said leg element is disengaged from said lock device, therebydestroying said four-pivotal-point linkage.
 11. The seat as claimed inclaim 10, which includes an adjustment device for adjustably positioningsaid seat in forward and rearward directions of the seat, wherein saidadjustment device comprises: a lower rail element fixedly mounted onsaid floor; and an upper rail element slidably engaged with said lowerrail element, wherein said lower end of said seat back frame ispivotally connected to said upper rail element, so that said firstpivotal point is defined between said lower end of said seat back frameand said upper rail element.
 12. A seat for use with a vehicle having afloor therein, wherein said seat comprises: a seat cushion; and a seatback foldable forwardly and downwardly onto said seat cushion,comprising: a seat slide device operable for adjustment in position ofsaid seat in forward and rearward directions of the seat, said seatslide device including: a lower rail element fixedly mounted on saidfloor; and an upper rail element slidably engaged with said lower railelement; a seat back frame provided in said seat back, said seat backframe being at a lower end thereof pivotally connected to said upperrail element of said seat slide device, thus defining a first pivotalpoint between said seat back frame and said upper rail element; a seatcushion frame provided in said seat cushion, said seat cushion framebeing at a rearwardly-facing end thereof pivotally connected to saidseat back frame, thus defining a second pivotal point between said seatcushion frame and said seat back frame; a leg element having an upperend pivotally connected to said seat cushion frame, thus defining athird pivotal point between said upper end of said leg element and saidseat cushion frame; and a lock device fixedly disposed at a locationsubstantially corresponding to said upper rail element; and an auxiliaryleg element provided to a bottom side of a forwardly-facing end portionof said seat cushion frame so as to be suspended from a bottom side ofsaid seat cushion; wherein a lower end of said leg element is releasablyengaged in said lock device, thereby being normally in a locked relationwith said floor, thus defining a fourth pivotal point between said lowerend of said leg element and said side of the floor, wherein said first,second, third and fourth pivotal points establish a four-pivotal-pointlinkage among said seat back frame, said seat cushion frame, said frontleg element and said floor, wherein said four-pivotal-point linkage isnormally maintained, and wherein, when said seat back frame is rotatedforwardly and downwardly by a first angle relative to said first pivotalpoint, said auxiliary leg element is brought into contact with saidfloor, with said lower end portion of said leg element being engaged insaid lock device, after which, when said seat back frame is furtherrotated forwardly and downwardly relative to said first pivotal point bya second angle exceeding a predetermined angle with reference to saidfirst angle, said lower end of said leg element is disengaged from saidlock device, thereby destroying said four-pivotal-point linkage.